In general, an apparatus and a method for detecting a decrease in air pressure of a tire mounted on a vehicle may be largely divided into two categories, and one is a direct tire pressure monitoring system (TPMS) and the other one is an indirect TPMS.
The direct TPMS as a type in which a sensor is mounted on the tire to perform the pressure of the tire has an advantage in which accurate pressure can be measured, while since the direct TPMS is constituted by various components including a pressure measurement sensor unit and a wireless unit for generally transmitting a measurement value in a wireless manner, and the like, the direct TPMS is higher in price and failure rate than the indirect TPMS. An example of the direct TPMS is U.S. Registration Pat. No. 4,695,823.
Meanwhile, the indirect TPMS is a type that estimates a loss of the air pressure by using a wheel sensor that is mounted on the vehicle to measure a wheel speed. The indirect TPMS has higher prices competiveness than the direct TPMS, but has a problem in which since a resonance frequency varies according to the wheel speed, accuracy slightly decreases.